1. Field of the Invention
The present invention relates to a sheet feeding apparatus for use in apparatuses such as a copying machine and a printer, which sucks and feeds sheet of papers, and more particularly, to a sheet feeding apparatus in which seat floating means floats one topmost sheet separately from a stack of sheets which is contained within sheet stacking means and suction transportation means sucks and feeds the floated sheet.
2. Description of the Related Art
In general, in a copying machine, a printer, etc., a sheet of paper is used as a paper on which an image is to be formed, a stack of sheets is housed in a sheet feeding cassette, and when an image is created, sheets are fed to a predetermined position for image creation one by one through a conveying path.
As a sheet feeding apparatus for feeding sheets one by one from a sheet feeding cassette, there are an apparatus which uses sheet feeding rollers, an apparatus which uses suction feeding means, and the like.
In an apparatus which uses suction feeding means, using a fan which rotates when driven by a motor as a drive source, air is blown onto a stack of sheets in a sheet feeding cassette to float the topmost sheet, and the topmost sheet which is floated is sucked and transported on a suction transportation belt.
A prior art disclosed in Japanese Unexamined Patent Publication JP-A 61-155139 (1986), for instance, is a technique for preventing wrinkles which are associated with scattering or excessive floating of sheets when the amount of a stack of sheets is small, in which a floating amount restricting member which moves in accordance with the amount of the stack of sheets is disposed above the stack of sheets, and the floating amount restricting member abuts a top surface of the stack of the sheets during sheet feeding so that even when the amount of the stack of sheets decreases, the floating amount restricting member stays abutting the top surface of the stack of sheets. According to the prior art, air is blown onto the stack of sheets from a side surface side downstream along a direction of transporting sheets to separate the bottom-most sheet from the rest of the stacked sheets, and the bottom-most sheet is sucked to the transportation belt and fed.
In a sheet feeding apparatus as described above in which air is blown onto the sheets to float the topmost or the bottom-most sheet and the sheet is sucked and transported by means of suction air (intake air), due to factors such as inherent variations in capability of a motor for a fan for blowing and sucking air, a motor for driving the suction transportation belt and the like, an external atmospheric pressure, and attaching of duct, the blowing force and the suction force upon the sheets become unstable, so that during suction attraction to the suction transportation belt, the sheets are not sucked parallel to the transportation direction but are sucked displaced, and therefore, a paper feeding error (jamming) can result.
This paper feeding error occurs particularly often in the case of sheets of a small size, since when the size of sheets is small, a sheet which is floated by blown air is positionally displaced.
Further, the related art which is disclosed in the publication requires to suck, float and feed the bottom-most sheet. The floating amount restricting member abuts the top surface of the stack of sheets, to prevent scattering of the sheets and creasing of the sheets due to excessive floating when the amount of laid sheets becomes small, but does not aim at preventing such a paper feeding error above which particularly occurs with feeding of sheets of a small size.